7 Answers
7

The leading word (not important which one you choose) gets attention to the question itself. To make the question polite, it's important to give it a polite pronunciation. I would not tell the guy that he's busy, he knows it himself.

Unabhängig, wie du jemanden unterbrichst, bedenke, dass du es schon in dem Moment getan hast, wenn du sowas wie Do you have a minute? sagst/fragst. Nicht selten bekommst du eine Antwort in der Form: "Eigentlich nicht, aber jetzt hast du mich ja schon unterbrochen."(Independent of the way you interrupt someone, pay attention on the fact that you already did, even just asking Do you have a minute?. It's not infrequently to get an answer alike: "No I didn't but you already bother me.")

(The latter is formed by simply omitting the first syllable and is slightly colloquial.)

This would not be considered rude (by anybody I know). Although you could certainly manage to intonate it such that it sounds a bit demanding, but you can do this with basically everything. As long as you put it clearly as a question it should be okay.

Use these Phrases - I am Sampath - English Teacher
May I speak with you for a moment?
Can I have a word with you?
Can I talk to you for a minute?
Can I talk to you?
May I have a moment with you?
Do you have a minute?

May I have a moment?
Can I have a minute?
May I be excused?
Excuse me for a moment.

On sales calls, I use in English, "May I stop you from working for two minutes?", which I will translate quite badly into German as "Mög ich Ihnen abstellen vun arbeiten auf zwei minuten?" There are the occasional jackasses who will answer rudely, but it shouldn't bother you. I just turn and walk away.